Explosive edge-forming



May 4, 1965 P. B. BARNETT ETAL 3,131,327

EXPLOSIVE EDGE-FORMING Filed April 10, 1961 2 Sheets-Sheet 1 INVENTOR. Fig LOUIS H. KNOP PAUL B. BARNETT Ema A TTOR/VE Y May 4, 1965 INVENTOR. LOUIS H. KNOP PAUL B. BARNE BY ATTORiY United States Patent M 3,181,327 EXPLOSIVE EDGE-FURMING Paul B. Barnett and Louis H. Knop, Glendon-a, Calih, assignors to Aerojet-General Corporation, Azusa, Calif, a corporation of Ohio Filed Apr. 10, 1961, Ser. No. 101,859 ill Claims. (El. 72-56) This invention relates generally to metal forming and more particularly to an explosive edge-forming process for metal. 1

In the past, methods of forming peripheral flanges, or beads, on metal sheet or plate, or methods of forming rings, or flaring in metal, required complex and expensive machinery and time-consuming heat treatments. The necessary machinery and the heat treat ovens were generally massive to permit working with metal in a wide variety of sizes and they occupied a considerable amount of costly plant space. All this further increased the cost of operation. In addition, because of the high cost of tooling, prior metal forming techniques were not satisfactory where the metal had to be formed into unusual and complex shapes or where the metal was large in size. It is apparent that less expensive, more compact, and more rapid metal forming devices and techniques would be very useful, and to provide such devices and techniques is the principal object of this invention.

In its principal aspect, the invention is practiced by placing a metal blank on a die having a peripheral forming or female die surface. The edge portions of the metal blank are unsupported and overlap the die. The peripheral forming surface of the die is at an angle to the overlapping edge portions of the metal. The die and the metal blank are immersed in a fluid and then an explosive charge is detonated in the fluid near the blank, producing a shock wave. Channeling devices are positioned in the fluid near the die. These channeling devices are shaped so that as the unsupported edge portion of the metal bends under the impact of a shock wave, the channeling devices bend or steer the shock wave and cause it to bear transversely against the bending edge portions of the metal. This continues until the bending edge portions of the metal engage the peripheral forming surface of the die. In this way, very little energy in the shock wave is lost by leakage past the bending edges of the metal and the bending efliciency of the shock wave is high.

Other objects and aspects, features, and advantages of the invention will be apparent to those skilled in the art, from the following more detailed description taken in conjunction with the appended drawings wherein:

FIG. 1 is a side sectional view of the apparatus used to fabricate metal parts by explosive forming;

FIG. 2 is a perspective view of a metal blank used with the apparatus disclosed in FIG. 1;

FIG. 3 is a partial perspective view disclosing both the die and the typcial arrangement of the various shock wave channeling elements used to shape the metallic blank; and

FIG. 4 is a perspective view of the completed metal piece after the operation of the explosive forming apparatus on the metal blank shown in FIG. 2.

Referring now to FIG. 1 of the drawing, the apparatus for edge-forming sheet metal indicated generally by the reference numeral 14 comprises a liquid holding container indicated generally by the reference numeral 12. The container may include a removable lid 14, side walls 16, and a supporting base 18. A die support plate 29 in the container rests on the supporting base 18 by means of supporting blocks or legs 22. In this particular embodiment, the die support plate 20 is provided with a centrally disposed recessed portion 24. Support mem- 3,181,327 Patented May 4, 1955 bers 26 and 28 project up from the base 29 of the recessed portion 24 and these members are provided with transverse openings 30 and 32 extending therethrough, for reasons to become apparent below (see FIG. 3).

The apparatus includes a die indicated generally by the reference numeral 34. The die is formed from a suitable metal plate and the shape of the die is dependent on the desired shape of the portion of the metal to be formed. In the present embodiment and by way of example, flanges are to be formed on the edges of a sheet metal blank 36 and flaring or short leg tubing is to be formed around the rim of an opening 38 in the blank 36 (see FIG. 2). The periphery of the edges of the sheet metal blank shown in FIG. 2 have a reverse curve and are parallel to each other for purposes of illustration, but it is to be understood that the principles of this invention can be applied to sheet metal having any shape. Similarly, opening 38 in the metal blank is shown as circular, and the edge portion 42 as seen in FIG. 4 is shown as right angle flaring or tubing for purposes of illustration.

To form the right angle flanges 40, and short leg tubing 42, shown in FIG. 4, it is necessary for die 34 to be shaped so its outer peripheral surface 44 serves as the female die surface. (See FIGS. 1 and 3.) In addition, the formation of short leg tubing around the edge of opening 38 shown in FIG. 2 requires a similarly shaped and somewhat enlarged opening 46 to be formed in the die 34, as best seen in FIG. 3. The inner peripheral surface 48 comprising the wall of die opening 46 is also a female die surface.

As seen in FIG. 1, the female die surfaces 44 and 48 are transverse to the upper supporting surface 50 of the die. With this arrangement, the marginal or edge portions 40, 4t), and 42, shown in FIG. 4 will be transverse .to the main body of the metal. Consequently, the angular relationship between the main body of the metal blank 36 and the edge portions to be formed can be varied as desired by controlling the angular relationship between the upper supporting surface 50 of the die and the peripheral forming surfaces 44 and 48.

For reasons to become apparent below, shock wave channeling devices comprising a mandrel 52, and peripheral guide members 54 are mounted on support plate 20 with die 34 (see FIGS. 1 and 3). The portions of the peripheral guide surfaces 54 adjacent the outer peripheral forming surfaces 44 of die 34 are recessed at 56, as shown in FIG. 1. These recessed portions 56 of the guide surfaces 54 are parallel to the peripheral edge of the blank 36 for reasons to become apparent below. Similarly, the surfaceof mandrel 52 adjacent the peripheral forming surface 48 of the hole 46 has recessed guide portions at 57.

The lid 14 shown in FIG. 1 is optionally provided with a shock wave reflector element 60. In addition, the lid may be provided with a suitable support element 62 for holding a high explosive material 64 such as TNT, sensitized liquid nitro methane, lump coal, composition C-4, gelatin strength), gelamite, etc. in a fixed position in the container.

In operation, the blank metal 36 to be formed is positioned as shown in FIG. 1 on the upper surface 50 of die $4 (see FIG. 1). The peripheral edges of edge portions 44), 4t), and edge portions 42 overlap forming or die surfaces 44 and 48 and are sealed to an adjacent surface 58 of the peripheral guide surfaces 54 and to the surface of the mandrel 52 by means of a suitable glue or putty 66. Next, the container is filled with a liquid such as water, to a depth sufficient to cover the high explosive 64 and the shock wave reflector 60. The glue or putty 66 on the edges of the sheet metal prevents the liquid from running into the region 72 between the recessed portions 56 of the peripheral guide surfaces 54,

the female die surfaces 44, and the inner surface of the edge portion 40 of the blank. Similarly, liquid is prevented from entering the region 74 between the female die surface 48 and the recessed surfaces 57 of the mandrel beneath the inner surface of the blank 36. Next, the air in regions 72 and 74 and in the recessed portion 24 of the die support plate is evacuated by means of vacuum tubing 70 connected at one end to passageway 63 in the die support plate 20 and connected at the other end to a vacuum pump (not shown); (see FIG. 1). After this, the high explosive 64 is detonated.

The detonation of the high explosive 64 produces a high velocity shock wave, indicated by fine lines 73, in the liquid 71. This shock wave expands spherically, but the portion of the shock wave expanding toward the metal blank 36 first encounters the conical tip 53 of mandrel 52. The interaction between the mandrel 52 and the shock wave channels or steers the shock wave against the edge portions 42 around hole 38 in blank 36. The shock wave acts as a male die member and bends the edge portions 42 from their initial solid line positions to the successive dotted line positions shown in FIG. 1. This continues until edge portions 42 are finally forced against female die surfaces 48. It is apparent that the recessed portions 57 on the mandrel are shaped to permit the edge portions 42 of the metal blank to bend, as shown in FIG. 1. In addition, however, they limit the space between the edge of the bending portion of the metal and the mandrel to prevent a substantial portion of the energy in the shock wave from passing by the bending portion and being wasted. Besides this, the conical shape of the mandrel 52 and the concave curvature of the recessed portion 57 channels or steers the shock wave so it is continually directed transverse to the bending edge portion 42. With this arrangement, a high percentage of the energy in the portion of the 'shock wave acting on the metal is utilized.

Of course, as the edge portions 42 of the metal are bent under the impact of the shock wave, the glue or putty sealing the edge of the metal to the mandrel is broken, permitting liquid 71 to flow into region 74. However, the shock wave moves substantially faster than the entrance of the liquid into region 74, so the edge portions of the metal being bent are still in a vacuum. It is noted that if region 74 were filled with a liquid, its incompressible characteristics would prevent a substantial portion of the energy in the shock wave from being utilized to bend the metal.

Edge portions and 40' of the blank are bent the same way as edge portions 42. Under some circumstances, however, it may be desirable to augment the effect of the shock wave by the use of the reflector element 60.

the shock wave energy to form the various parts of the metal blank.

As described in connection with the mandrel 52 and recessed portions 57,'the surfaces of the recessed portions 56 either graze or are closely adjacent to the free edges of the bending edge portions 40 and 40'. With this arrangement, the shock wave bearing against the end portions 40 and 40' cannot escape past these edge portions to become dissipated. In addition, the recessed portions 56 of the peripheral guide surfaces 54 channel and steer the shock wave so it is always directed generally transverse to the bending edge portions of the sheet metal during the formation of the flanges for a more eflicient utilization of the energy in the shock wave.

It-is noted that the flanges or formed edges 40 and 40 (shown in FIG. 4) differ (for purposes of illustration) in that a bead 41 is formed on the free edge of flange portion 40', whereas no bead is formed on the free edge of flange portion 40 (as seen in FIG. 1). To form a bead or other bend on the end of a flange, it is necessary only to shape the recessed portions 56 so that as edge portion 49' is deflected by the force of the shock wave, its tip grazes the concave surface of the recessed portion 55. This grazing encounter forms the bead 41 on flange 40', as shown in FIG. 4. Flange 40, in this particular embodiment, is not provided with a head because its free end does not engage any part of a surface of the recessed portion 56, as it bends under the impact of the shock wave.

Obviously, the degree of engagement between the edges of edge portions 40 and 4t) and the surface of the recessed portion 56 controls the shape of the bead or free end flange 41. Consequently, by controlling the extent of this engagement, a wide variety of beads or free end flanges can be formed.

While the preferred embodiment of the material and apparatus of the present invention have been specifically disclosed and illustrated in the specification and accompanying drawings, it is to be understood that the described embodiment is not a limitation of the invention, since various modifications may be made therein by those skilled in the art without departing from the scope of the invention as defined by the appended claims.

We claim:

1. A method of edge-forming material comprising the steps of supporting the surface of the material, except the edge portions to be formed, on a die with a peripheral forming surface, immersing the material and the die in a fluid, initiating a shock wave in the fluid, channeling the shock wave against the unsupported edge portions of the material, and forcibly bending the unsupported edge portions by the shock wave into engagement with the peripheral forming surface of the die so that when the shock wave acts against the unsupported edge portions of the material, it forcibly guides the periphery of the unsupported edge portions of the material along respective curved surfaces of a corresponding guide member adjacent thereto to prevent dissipation of the shock wave past the periphery of the unsupported edge portions of the material.

2. The method of edge-forming material described in claim 1 including the step of initially evacuating the region between the edge portions of the material and the peripheral forming surface of the die.

3. A method of edge-forming metal comprising the steps of positioning the metal on the surface of a die with the edge portion to be formed lying unsupported over the peripheral edge of the die, immersing the die and metal in a liquid, producing a shock wave in the liquid, channeling the shock wave against the unsupported edge portion of the metal and directing it generally transverse thereto while maintaining the liquid beyond the unsupported edge in an untrapped condition and free to move past said edge, and forcibly bending the unsupported edge portion of the metal into engagement with the peripheral edge of the die by striking the unsupported edge portion of the metal with the shock wave, while guiding the edge of the unsupported edge portion of the metal along a curved surface of a guide member adjacent thereto to prevent dissipation of the shock wave past the edge of the unsupported edge portion of the metal.

4. An apparatus for flaring the peripheral edge of an opening in sheet metal comprising in combination a container for holding a fluid, means for holding a high explosive material in a predetermined position in said container, a die support in said container, a die mount on said die support with the periphery of the die serving as a forming surface, a mandrel mounted on said die support and adapted to extend through the opening in the sheet metal, said mandrel having guiding portions defining a peripheral surface thereon adjacent the opening so when the shock wave produced by the detonation of said high explosive material bears against the mandrel, the shock wave is deflected thereby into transverse engagement with the edges of the opening in the metal to bend the edges of the sheet metal along the guiding portions and into engagement with the forming surface of the die.

5. An apparatus for edge forming sheet metal, comprising in combination a container for holding a liquid, means for holding a high explosive material in a predetermined position in said container, a die support in the container, a die mounted on said die support with the peripheral surfaces of the die shaped to serve as a female diemember, at least one shock wave steering device in said container, means for initially evacuating the region between the surface of the edge portion of the sheet rnetai, the peripheral surfaces of the die, and a surface of the steering device, at least a portion of said steering device positioned adjacent to and parallel with the peripheral edge of the sheet metal to guide said peripheral edge along said portion upon production of a shock wave by the detonation of said high explosive material, at least a part of any shock wave produced by the detonation of said high explosive material being continually steered and maintained generally transverse to the edge portion of the sheet metal as the edge portion of the sheet metal is bent and forced into engagement with the peripheral surfaces of the die, whereby a high proportion of the energy in the portion of the shock Wave bearing against the edge portion of the sheet metal is utilized in forming the edges of the sheet metal.

6. A method of edge-forming material comprising the steps of supporting the surface of the material, except at least one marginal portion to be formed, on a die having a peripheral forming surface, immersing the material and the die in a fluid, initiating a shock wave in the fluid, channeling the shock wave against the unsupported marginal portion of the material, and forcibly bending the unsupported marginal portion of the material into engagement with the peripheral forming surface of the die by striking the unsupported marginal portion of the material with the shock wave, While guiding the edge of the unsupported marginal portion of the material along a curved surface of a guide member adjacent thereto to prevent dissipation of the shock wave past the edge of the marginal portion of the material.

7. A method of edge-forming material along marginal portions thereof and an opening in the material comprising the steps of supporting the surface of the material, except the portions to be formed, on a die having respective peripheral forming surfaces, immersing the material and the die in a liquid, initiating a shock wave in the liquid, channeling the shock wave against the unsupported portions of the material, and forcibly bending the unsupported portions of the material into engagement with respective forming surfaces of the die by striking the unsupported portions of the material with the shock wave, while guiding the edges of the unsupported portions of the material along respective curved surfaces of a corresponding guide member adjacent thereto to prevent dissipation of the shock wave past the edges of the unsupported portions of the material, the liquid beyond the guided edges being maintained in an untrapped free to move condition throughout edge-forming.

8. An apparatus for edge-forming material along marginal portions thereof and an opening in the material comprising, in combination, a container for holding a liquid, means for holding a high explosive material in a predetermined position in said container, a die sup ort in the container, a die adapted to support the material except the portions thereof to be formed, said die being mounted on the die support with the peripheral surfaces of the die shaped to serve as forming surfaces, a mandrel mounted on the die support and adapted to extend through the opening in the material, said mandrel shaped so its peripheral surfaces adjacent to the edge of the opening in the material serve as guiding surfaces, said mandrel further shaped so when the shock wave produced by the detonation of the high explosive bears against the mandrel, the shock wave is deflected thereby into transverse engagement with the edges bounding the opening in the material, and a pair of guide members respectively positioned on said die support at each side thereof in outwardly disposed relation to the opposite sides of said die, each of said guide members being shaped so its peripheral surface adjacent to the marginal portion corresponding thereto serves as a guiding surface so that when the shock Wave strikes the unsupported portions of the material, the peripheral edges of the unsupported portions are guided along respective guiding surfaces to prevent dissipation of the shock wave past the edges of the unsupported portions of the material, the liquid against which the peripheral edges are moved by the shock Wave being free to move away therefrom and prevent the buildup of significant back pressure against said edges.

9. The method of flaring the periphery of an opening in metal comprising the steps of positioning the metal having an opening therein on a surface of a die with the edge portion of the metal surrounding the opening lying unsupported over a hole in the die, immersing the die and metal in a liquid, initially preventing the entrance of said liquid in the region between a surface of the unsupported edge portion of the metal and the peripheral Wall surface of the hole in the die, producing a shock wave in the liquid, channeling the shock wave against the unsupported edge portion of the metal and maintaining it generally transverse thereto so that the shock wave acting as a male die member bends the unsupported edge portion of the metal surrounding the opening against the peripheral wall surface of the hole in the die to form the flaring.

10. The method of flaring the periphery of an opening in metal comprising the steps of, positioning the metal having an opening therein on a surface of a die with the edge portion of the metal surrounding the opening lying unsupported over a hole in the die, immersing the die and metal in a liquid, initially evacuating the region between a surface of the unsupported edge of the metal and the peripheral wall surface of the hole in the die, producing a shock wave in the liquid, channeling the shock wave against the unsupported edge portion of the metal andmaintaining it generally transverse thereto so that the shock wave acting as a male die member bends the unsupported edge portion of the metal surrounding the opening against the peripheral Wall surface of the hole in the die to form the flaring.

References Cited by the Examiner UNITED STATES PATENTS 2,422,883 6/47 Bruderlin 113-44 2,458,842 l/ 49 Evensen 15 3-25 2,969,758 1/61 Hewlett et a1. 1l344 2,983,242 5/61 Cole 11344 3,044,430 7/62 Zeigler 29421 3,057,313 10/62' Setser 29-421 3,068,822 12/62 Orr et al 1l3-44 FOREIGN PATENTS 105,422 9/42 Sweden.

OTHER REFERENCES Explosives Form Space Age Shapes, Steel, Aug. 25, 1958; pages 8286.

Explosive Forming, American Machinist, June 15, 1959, vol. 103, No. 12; pages 127-138.

CHARLES W. LANHAM, Primary Examiner.

WHITMORE A. WILTZ, NEDWIN BERGER,

Examiners. 

1. A METHOD OF EDGE-FORMING MATERIAL COMPRISING THE STEPS OF SUPPORTING THE SURFACE OF THE MATERIAL, EXCEPT THE EDGE PORTIONS TO BE FORMED, ON A DIE WITH A PERIPHERAL FORMING SURFACE, IMMERSING THE MATERIAL AND THE DIE IN A FLUID, INITIATING A SHOCK WAVE IN THE FLUID, CHANNELING THE SHOCK WAVE AGAINST THE UNSUPPORTED EDGE PORTIONS OF THE MATERIAL, AND FORCIBLY BENDING THE UNSUPPORTED EDGE PORTIONS BY THE SHOCK WAVE INTO ENGAGEMENT WITH THE PERIPHERAL FORMING SURFACE OF THE DIE SO THAT WHEN THE SHOCK WAVE ACTS AGAINST THE UNSUPPORTED EDGE PORTIONS OF THE MATERIAL, IT FORCIBLY GUIDES THE PERIPHERY OF THE UNSUPPORTED EDGE PORTIONS OF THE MATERIAL ALONG RESPECTIVE CURVED SURFACES OF A CORRESPONDING GUIDE MEMBER ADJACENT THERETO TO PREVENT DISSIPATION OF THE SHOCK WAVE PAST THE PERIPHERY OF THE UNSUPPORTED EDGE PORTIONS OF THE MATERIAL. 